[1] https://wiki.linaro.org/Boards/BeagleBoard-X15#Boot_from_SD_card

# Search for "FLASHING U-BOOT TO EMMC" on the webpage [1]...

Target:
=> env default -f -a
=> setenv partitions $partitions_android
=> env save
=> fastboot 1

Host:
$ sudo fastboot flash xloader MLO
$ sudo fastboot flash bootloader u-boot.img
reboot target and redo => fastboot 1 on target...
$ sudo fastboot flash userdata rpb-console-image-am57xx-evm-20180122023353-571.rootfs.img

set bootargs to:
# bootargs=run findfdt; setenv console ttyS2,115200n8; setenv mmcdev 1; setenv bootpart 1:f; run mmcboot
=> setenv bootargs 'run findfdt; setenv console ttyS2,115200n8; setenv mmcdev 1; setenv bootpart 1:f; run mmcboot'
=> saveenv

# try to dd over the img file then resize the sd-card with scripts in /opt/scripts/tools/